The present invention relates to a zoom lens, particularly having interchangeable relay lenses in which a magnifying attachment is inserted so as to change the range of the variable focal length.
Methods and means for changing the range of the variable focal length of a photographic camera or a television camera without dismounting the zoom lens in U.S. Pat. No. 4,015,895 or Ser. No. 692,518, now U.S. Pat. No. 4,240,697, U.S. Pat. No. 4,157,211, U.S. Pat. No. 4,146,305 and Ser. No. 28,442.
As in the present invention an attachment lens can be mounted between the zoom section and the photo-detecting surface in such a manner that the range of the variable focal length can easily be changed.
On the other hand, the taking lens has various picture sizes in accordance with the film to be used or the size of the pick-up tube. For example, in a 35 mm still picture camera the maximum image height Y=21.635, in super 8 motion picture camera Y=3.58 and in a 1" pick-up tube Y=8.0. It is very often difficult from the economical or other reasons to prepare the zoom lenses which fit to all the picture sizes. Hence it is possible to use one zoom part in common with several relay lenses by exchanging them for each other. What is important with such kind of interchangeable relay lenses is that the light beam passing through the focusing lens group as well as the movable lens group at the time of zooming has to be unchanged regardless of the exchange of the relay lenses. Consequently, the focal lengths and the F numbers are changed so as to keep the picture angle constant. Therefore, it is essential that EQU Focal length f.sub.2 =(Y.sub.2 /Y.sub.1)f.sub.1, f.sub.3 =(Y.sub.3 /Y.sub.1)f.sub.1, EQU F number F.sub.n2 =(Y.sub.2 /Y.sub.1)F.sub.n1, F.sub.n3 =(Y.sub.3 /Y.sub.1)F.sub.n1,
Here, the maximum image height of each picture size is Y.sub.1, Y.sub.2, Y.sub.3 . . . , the focal length f.sub.1, f.sub.2, f.sub.3 . . . and F number F.sub.n1, F.sub.n2, F.sub.n3 . . . .